(1) Field of the Invention
The invention relates generally to electronic circuits for higher voltages and in particular to comparator circuits realized with integrated-circuit technologies.
(2) Description of the Prior Art
Particularly designed special comparator circuits in electronic applications are required, when it comes to comparing higher voltage levels of e.g. measuring signals and reference signals for sensors and actuators. This is a noted and quite common requirement for electronic circuits as used in the automotive industry, for example. There are very often strong voltage spikes on data lines to be handled, especially when connections to the battery of the car are considered, with its heavy load switching during normal operations. Therefore the handling of higher voltage levels is an elementary demand.
Realizations of the prior art for such comparator circuits are often implemented as specifically tailored semiconductor circuits, fulfilling the operational demands regarding the higher voltages or currents supplied. Therefore, when a direct voltage comparison takes place sometimes DMOS (double diffused) transistor devices are used, making necessary an expensive process in semiconductor fabrication. Alternatively CMOS devices with extended drain realizations are employed, but when used in a differential input pair transistor configuration, high VGS (Gate-Source) values for the transistors have to be specified, which leads also to more expensive components. Furthermore these comparators have to be interconnected with some logic circuitry, which is controlling the overall operation of the electronic circuits incorporating the comparator. These logic circuits or even microprocessor systems normally are working with low voltages. The composition of these two voltage domainsxe2x80x94one for higher, the other for lower voltagesxe2x80x94has to be made in such a way, that no detrimental influences are affecting onto each other. Thereto an appropriately combined semiconductor technology capable of handling all these demands is chosen, which most often leads to costly solutions. It is therefore a challenge for the designer of such circuits to achieve a high-quality, but lower-cost solution. There are various patents referring to such solutions.
U.S. Pat. No. (6,377,075 to Wong) describes a high voltage protection circuit on standard CMOS process wherein a circuit topology is disclosed for avoiding transistor gate oxide-dielectric breakdown and hot-carrier degradation in circuits, such as CMOS inverters, fabricated in a standard sub-micron CMOS process with feature size below 0.8 xcexcm and gate-oxide thickness less than 150 xc3x85. An inverter circuit according to the invention incorporates four transistors appropriately biased, additional to those of a standard inverter circuit (comprising two transistors), in order to avoid hot-carrier degradation and gate-oxide breakdown. The invention is also applicable to transistor circuits having other functionalities for example logic level translators.
U.S. Pat. No. (6,424,183 to Lin, et al.) discloses a current comparator realized in a low voltage CMOS process, where the presented invention discloses a current comparator having simple, cheap and fast characteristics, especially discloses a current comparator having a small dead zone and excellent driving capability.
U.S. Pat. No. (6,452,440 to Rapp) shows a voltage divider circuit, wherein a charge pump system includes a charge pumping circuit for outputting a high voltage Vpp at a node. An oscillator circuit, coupled to the charge pumping circuit, drives the charge pumping circuit with at least one clock signal. A current source generates a pulldown current. A voltage divider circuit is coupled between the node and the current source. The voltage divider circuit cooperates with the current source to form a feedback loop for controlling the oscillator circuit to run at variable, optimum frequency for controlling the rate-of-rise and the amplitude of the voltage Vpp while minimizing power-supply current drain.
A principal object of the present invention is to provide an effective and very producible method and circuit for comparing voltage signals of higher input levels.
Another further object of the present invention is to replace a comparison of voltages by a comparison of currents.
Another still further object of the present invention is to reach a transformation of high-voltage signals into current signals at lower voltages.
A still further object of the present invention is to reduce the power consumption of the circuit by realizing inherent appropriate design features.
Another object of this invention is its producibility as a monolithic semiconductor integrated circuit.
Also an object of the present invention is to reduce the cost of manufacturing by implementing the circuit as a monolithic integrated circuit in low cost CMOS technology.
Also another object of the present invention is to reduce cost by effectively minimizing the number of expensive components.
In accordance with the objects of this invention, a method for realizing a high voltage comparator is presented. Said method includes providing a voltage to current conversion stage branch for the VInp signal, a voltage to current conversion stage branch for the VRef signal, a reference signal providing circuit, and a current comparator block, generating an output signal. Also included in said method is transforming static high supply voltage levels into static currents as well as transforming a high-voltage input signal into a proportional current signal and transforming a high-voltage reference into a proportional current reference. Further comprises said method combining said static currents and proportional current signals into two resulting current input signals and feeding said resulting current input signals into a current comparator circuit operating in the low-voltage domain. Equally included in said method is comparing said current input signals within said current comparator circuit and generating a low voltage output signal representing the result of said high input voltage comparison.
Also in accordance with the objects of this invention, a circuit, capable of comparing higher voltage signals is achieved and which generates an output signal for follow-up processing in the low-voltage domain. Said circuit comprises means for transforming a static high voltage supply level into static currents, as well as means for transforming a high voltage input signal into a proportional current signal and means for transforming a high voltage reference into a proportional current reference. Further on includes said circuit means for combining said static current and said proportional current signal into a resulting current input signal and also means for combining said static current and said reference current signal into a resulting reference current input. Also incorporated are means for feeding said resulting current input signal and said reference current into a current comparison circuit, which serves as means for comparing said current input signal and said reference current, designated as current comparator. Finally comprises said circuit means for generating a low voltage output signal describing the relation of said high voltage input signal and said reference input to each other.